CHANGES OF FOOD IN THE ALIMENTARY CANAL. 



145 



FIG. 63. 



and form exquisitely fine threads, with swellings or varicosities upon them, 

 which lie has been able to trace into direct continuity with the altove-men- 

 tioned prolongations of the epithelial cells, several passing into each cell. 

 The development of the salivary glands commences during the second half 

 of the second month, in accordance with the general plan of the aciuous 

 glands, by a simple protrusion of a part of the wall of the oral cavity, which 

 subsequently gives off budlike processes. 



102. Numerous researches have shown, that the characters of the fluids 

 poured forth respectively from the three principal glands are by no means 

 identical ; and that the buccal mucus has a 

 very important share in the operations of 

 that mixed product, which constitutes the 

 ordinary Saliva. The specific gravity of 

 this fluid may vary within the limits of health 

 from 1002 to 1009. The variations appear 

 to be partly referable to the amount of solids 

 and liquids ingested, and partly to the 

 amount of the secretion previously poured 

 out; but it may be in some measure attrib- 

 uted to a difference in the proportions of 

 the fluids poured into the mouth by the 

 several glands which secrete them. Mixed Saliva is found to contain a few 

 epithelial scales thrown off by the buccal mucous membrane, and a small 

 number of minute corpuscles proceeding chiefly from the lingual and ton- 

 sillitic glands, which perform curious spontaneous and Amoeba-like move- 

 ments. 1 Its reaction is always alkaline in health, which is due to the pres- 

 ence of the tribasic phosphate of soda; but the degree of alkalinity varies, 

 being greatest during and after meals, and least after prolonged fasting, 

 when the fluid is almost neutral. Its temperature at the moment of secre- 

 tion is always from 1 to 2 Fahr. higher than the arterial Blood supplying 

 the gland. 2 According to Oehl, 3 the saliva is secreted and discharged by 

 the parotid duct, under a pressure amounting at its maximum to a column 

 of water of six inches in height. The following are some of the chief 

 analyses of this fluid that have been made: 



Capillary Network around the Follicles 

 of the Parotid Gland. 



1 Brucke, Sitzungsbericht d. Wiener Akad . Bd. xlv. 



2 Kiihne, Phys. Chemie, 1866, p. 6. 3 La Saliva Umana, etc , Pavia, 1864. 

 4 Simon, Animal Chemistry, vol. ii, p. 4. 5 Donders's Phys., p. 188, 1859. 



6 See Canstatt's Jahresbericht, 1850, p. 136. 



1 Inaug. Diss., De Saliva, Dorpati, 1848. 



8 Brit, and For. Med.-Chir. Pvev., 1860, p. 207. 



